1. Field of the Invention
The present invention relates to a multi-plate clutch used in an automatic transmission of a vehicle and the like. More particularly, the present invention relates to a multi-plate clutch in which a relative relationship between urging portions of a piston and spline positions of driven plates are regulated.
2. Related Background Art
In a multi-plate clutch, a power is transmitted by engaging a plurality of friction engaging elements disposed within a clutch housing with each other. Within the clutch housing, a piston movable in an axial direction is provided for applying an axial urging force to the friction engaging elements to engage them with each other.
In the multi-plate clutch, it is designed so that driven plates (separator plates) and drive plates (friction plates), which serve to act as the friction engaging elements, are alternately arranged in an overlapped fashion, whereby the multi-plate clutch is engaged (tightened) or disengaged (released) by engaging the friction engaging elements with each other by the urging force of the piston or disengaging the friction engaging elements from each other.
When the piston of the multi-plate clutch urges the driven plates, due to a difference in stress between pawl portions (spline portions) and non-pawl portions of the driven plates, heat spots are generated. The heat spots are black spots generated on surfaces of the driven plates (separator plates) by means of engagement with high heat load. Since the heat spot portion is convex, the heat spot may attack the friction material. Accordingly, the heat spot may cause shudder or may affect a bad influence upon the operation and endurance of the clutch.
Further, if the splines of the driven plates are not positioned equidistantly, when the piston of the multi-plate clutch urges the driven plates, since there is difference in rigidity between the spline portions and non-spline portions of the driven plates, the driven plates may be deformed, with the result that the heat spots may partially be generated on urging surfaces corresponding to the non-spline portions.
In order to suppress the heat spot, Japanese Patent Application Laid-open No. 9-287622 (1997) discloses an arrangement in which, in order to make temperatures between plates uniform, thicknesses of driven plates are reduced steppingly from the driven plate nearest to a piston.
However, as shown in the above-mentioned Japanese Patent Application Laid-open No. 9-287622, the fact that a plurality of driven plates having different thicknesses are prepared for one multi-plate clutch may lead in increase in cost, thereby causing a new problem.